Click on image to enlarge. Kreg's one-piece design eliminates clogging and provides a much smoother and faster drilling stroke than the drill bits with replaceable center drills. The DKDB bit is made of cobalt steel that increases the bitís life. Because the DKDB bit is also 3/8" diameter it can be used in any of our other manual jigs as a premium replacement. Be sure to order the left hand drill bit (LH- DKDB) for the middle spindle of the DK3100 fully-automatic machine.